1. Field of the Invention
The present invention relates to a system for homogeneously mixing and forming plastic compositions into useful products, and more particularly to a system, including a method, for evenly dispersing a second polymeric material throughout the base plastic composition during plasticizing, mixing and extrusion into useful form.
Previously, it has been common practice to mix pigment particles into a plastic composition prior to extrusion by use of a screw conveyor, located within a plasticizer-extruder, which feeds the composition through a series of offset or staggered baffle plate mixing elements located at the distal end of the screw.
Plastic products manufactured by apparatus of the general type described have sufficient uniformity of coloration to satisfy many commercial requirements; however, the coloration may not be uniformly distributed throughout the plastic composition in its extruded state, particularly when output demand is high. Often pigment flow lines can be readily observed by visual inspection of the plastic products thereby produced. Also in the case of making plastic products such as sheet or film which is then oriented by stretching, the heat-shrinkage characteristics are limited to the thermal and physical limitations of the base material. Consequently, plastics produced by the above-described prior art procedure may fall below commercially accepted coloration and property standards for some types of products. Also, when other types of additives are introduced into the base material unless proper plasticizing, intermixing and extruding techniques are employed, the additives may not be uniformly dispersed to provide the desired properties attributable to the additives incorporated into the suitable plastic base material. Heretofore, there has been no effort to improve the heatshrink capability of foamed, oriented, polyolefin materials such as foamed polyethylene and foamed polystyrene by additives which enhance the infrared energy absorbing characteristics of the base material.